1. Field of the Invention
The present invention relates to a stereo camera and, particularly, to a stereo camera which is capable of shooting a subject in a close range by expanding the offset adjusting range at the time when the films are to be mounted.
2. Description of the Prior Art
FIGS. 6 and 7 are three-dimensional views of a stereo slide. When a distance between the centers of the right and left windows 2R and 2L of a stereo slide mount 1 is denoted by Pw and a distance between the centers of subject images of the right and left films mounted on the stereo slide amount is denoted by Pi, and when Pw=Pi as shown in FIG. 6, then, the subject image and a stereo window Iw (imaginary window in which the right and left windows appears to be in agreement as viewed in a three-dimensional way) appear at infinity.
It is unnatural when the stereo window Iw appears at an infinite position. It is rather natural when the stereo window Iw appears at a distance of several meters and the subject image is seen at the back of the stereo window Iw like when one looks at an outdoor scenery from the indoors through a window of a house.
FIG. 7 illustrates a state where the distance Pi between the centers of the right and left subject images is expanded to be larger than the distance Pw between the centers of the right and left windows, i.e., Pw less than Pi, to correct the parallax, where the stereo window Iw appears in a close range and the subject image is seen at a distance. The stereo window Iw appears closer with an increase in the distance Pi between the centers of the subject images.
A manual of stereo photography states that Pw+1.2 mm is a limit of expansion of the distance Pi between the centers of the subject images at infinity and, in this case, the subject images appears at infinity and the stereo window Iw appears at a distance of about 2 to 3 meters though it varies depending upon the focal distance of the photographing lenses, offering a natural three-dimensional feeling. When the distance Pi between the centers of the subject images is more expanded, however, the stereo window Iw appears in a close range, whereby the edges of the stereo window becomes unclear causing strain to the eyes.
There have heretofore been known a stereo camera having a zero lens offset in which the distance between the centers of the right and left photographing lenses is equal to the distance between the centers of the right and left film exposure windows, and a stereo camera of the lens offset-type in which the distance between the centers of the right and left photographing lenses is set to be smaller by about 1.1 mm than the distance between the centers of the right and left film exposure windows in order to correct the distance for setting the stereo window.
When the subject is infinitely distant, the rays of light incident on the right and left photographing lenses from the same point at infinity is in parallel with each other, and the distance between the centers of the subject images at infinity on the right screen and on the left screen on the films becomes equal to the distance between the optical axes of the right and left photographing lenses. When the subject at infinity is shot using the stereo camera having zero lens offset, therefore, the distance between the centers of the right and left infinite subject images on the films of the stereo camera is in agreement with the distance between the centers of the right and left screens.
In mounting the films which have shot the subject at infinity on the stereo slide mount, therefore, the pitch Pf for mounting the right and left films FR, FL must be expanded to be larger than the distance Pw between the centers of the right and left windows 2R, 2L of the stereo slide mount 1 as shown in FIG. 8a, so that the distance Pi between the centers of the subject images becomes larger as denoted by Pfmin than the distance Pw between the centers of the right and left windows as shown in FIG. 7. Here, the width of the windows of the stereo slide mount is narrower than the width of the screens of the films FR, FL, and the right and left ends of the films are masked.
Further, as the distance to the subject becomes small, the positions of the subject images on the right and left film exposure surfaces in the stereo camera are displaced outward, respectively, and the distance between the centers of the subject images increases. The images photographed on the films are inverted upside down and right side left. Therefore, the films are mounted on the stereo slide mount being turned by 180 degrees so as to obtain an erect image. As the distance to the subject decreases, therefore, the distance between the centers of the subject images on the stereo slide mount becomes small. Therefore, the films FL, FR that have shot the subject in a close range are mounted being offset outward more than the films that have shot the subject at infinity, and Pfmax becomes a limit of the shortest shooting distance as shown in FIG. 8b. The films photographed by using the stereo camera of the lens offset-type of which the pitch of the photographing lenses is contracted by about 1.1 mm from the pitch of the screens, have a contracted distance between the centers of the subject images that are photographed. Therefore, the distance Pi between the centers of the subject images expands in a state where the films are mounted being turned by 180 degrees on the stereo slide mount. Therefore, it is not almost necessary to offset the pitch for mounting the films. If the films are mounted in a manner that the distance Pf between the centers of the screens of the films FR and FL is nearly equal to the distance Pw between the centers of the right and left windows 2R and 2L of the stereo slide mount 1 as shown in FIG. 9a, the distance between the centers of the subject images at infinity is expanded to be larger by about 1.1 mm than the distance Pw between the centers of the right and left windows 2R and 2L, whereby the subject distant by more than about 2 meters appears to be farther than the stereo window Iw as shown in FIG. 7, and this state represents the closest positions Pfmin of the films.
When the subject of not farther than 2 meters is shot, however, the right and left films FR and FL must be mounted being offset outward to expand the pitch Pf as shown in FIG. 9b. As shown in FIG. 8b, therefore, the distance between the films can be expanded up to Pfmax.
As described above, the positions for mounting the films must be adjusted within a range in which the screens of the films are held in the windows of the stereo slide mount, to correct the feeling of distances relative to the stereo window and to the stereo picture. As shown in FIG. 8, however, the films photographed by using the stereo camera having zero lens offset can be adjusted for its distance only within a narrow range (Pfminxe2x88x92Pfmax). In many cases, therefore, the films photographing the subject in a close range are mounted without producing a suitable three-dimensional feeling, though it may differ depending upon the width of the windows of the stereo slide mount.
In the case of the stereo camera of the lens offset-type as shown in FIG. 9, the range for adjusting the distance between the films can be expanded to be wider than that of the case of FIG. 8. Even in this case, however, the films shoting the subject in a close range cannot be coped with.
Thus, there arises a technical assignment that must be solved to expand the range in which the distance between the films can be adjusted on the stereo slide mount and to obtain a proper three-dimensional effect even when shooting a subject in a close range. The object of the invention is to solve the above assignment.
The present invention was proposed to accomplish the above-mentioned object, and provides a stereo camera wherein the distance between the optical axes of the right and left photographing lenses is set based on the width of the screens of the stereo camera and on the width of windows of the stereo slide mount, so that the distance between the centers of the subject images at infinity on the right and left films becomes equal to the distance between the centers of the right and left windows of the stereo slight mount+(0.7 mm to 1.2 mm) when a pair of right and left films that are shot by using a stereo camera are mounted on a stereo slide mount at the closest positions within a range of adjusting the distance between the films.